Pipetting systems are widely utilized in laboratories and hospitals for withdrawing and dispensing relatively small, predetermined quantities of liquids from one location to another, such as between test tubes, microplates and other liquid receptacles. Portable, or hand-held, pipettors are one type of pipetting system. Hand-held pipettors generally include a housing, a cylinder including two cylinder ends, with one end positioned within the housing and the other end extending from the housing to form a pipettor tip holder, a piston that moves within the cylinder to withdraw liquid from a supply receptacle and dispense the liquid to a receiving receptacle, and a plunger that drives the piston. While not a permanent part of the pipettor, a disposable pipettor tip is commonly attached to the end of the tip holder to retain the liquid to be transferred. This tip can be removed from the tip holder, disposed of, and replaced with a new tip. These hand-held pipettors may be configured to transfer liquids by automated or manual actuation of the pipettor. Automatically operated hand-held pipettors generally include a motor for actuating the plunger to move the piston within the pipettor cylinder for liquid transfer. Manually operated hand-held pipettors require the pipettor user to apply force to the plunger head, usually with a thumb or a finger, to actuate the piston.
Hand-held pipettors may be designed as fixed volume pipettors, where only one predetermined liquid volume is withdrawn and dispensed, or as adjustable pipettors, where the user may set a desired volume to be dispensed within a given volume range. Stop features located within a pipettor determine the distance that a piston will travel, also known as the stroke. The stroke corresponds to the volume of liquid to be withdrawn and dispensed. Hand-held pipettors commonly include two stops to establish the limits of the stroke. For purposes of the foregoing description, these two stops will be referred to as a front stop and a rear stop. In this description, the front stop is the stop closest to the tip holder and the rear stop is the stop closest to the plunger head, or in a manual pipettor, the end of the plunger that is manually actuated by a pipettor user. The stops in a fixed volume pipettor are fixed, and the piston travels the same stroke during each complete actuation of the plunger. In an adjustable volume pipettor, at least one of the stops is movable to adjust the stroke length of the piston, and thus the volume to be withdrawn and dispensed.
In manual pipettor applications where the volume of liquid to be transferred may vary frequently within a single application, the pipettor user must frequently change the volume settings on the pipettor, which can cause fatigue and potentially inaccurate volume settings on the pipettor.